Risks of knee surgery 

In over 80% of cases, surgery to repair an anterior cruciate ligament (ACL) fully restores the functioning of the knee.

ACL surgery will improve the stability of your knee and stop it giving way. You should be able to resume normal activities after six months.

However, your knee may not be exactly like it was before the injury. You may still experience some pain and swelling in the replacement ligament. If other structures in your knee are also damaged, it may not be possible to fully repair them.

As with all types of surgery, there are some risks associated with knee surgery. They include:

  • infection – the risk of infection is small (less than 1%); you may be given an antibiotic after your operation to prevent infection developing
  • blood clot – the risk of a blood clot forming and causing problems is very low (about 1 in 1,000); if you're thought to be at risk, you may be given medication to prevent blood clots forming
  • knee pain – affects almost 2 in 10 of people who have ACL surgery and is more likely to occur when the patellar tendon is used as graft tissue; you may have pain behind your kneecap or when kneeling down or crouching
  • knee weakness and stiffness – some people experience long-term weakness or stiffness in their knee

After ACL surgery, there's also a small chance (less than 10%) that the newly grafted ligament will fail and your knee will still be unstable.

If the first operation is unsuccessful, further surgery may be recommended. However, subsequent operations are often more difficult and don't usually have the same long-term success rate as a first tendon repair.


Page last reviewed: 16/07/2015

Next review due: 01/07/2018